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Investments - Amortized Cost and Fair Value of Securities Available for Sale (Details) - USD ($) $ in Thousands | Jun. 30, 2019 | Dec. 31, 2018
--- | --- | ---
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | $ 331,519 | $ 182,325
Gross Unrealized Gains | 1,537 | 178
Gross Unrealized Losses | (1,515) | (6,258)
Available-for-sale investments | 331,541 | 176,245
Mortgage-backed securities |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 233,210 | 159,937
Gross Unrealized Gains | 1,196 | 155
Gross Unrealized Losses | (1,445) | (5,517)
Available-for-sale investments | 232,961 | 154,575
Utah Housing Corporation bonds |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 21,136 | 22,388
Gross Unrealized Gains | 181 | 23
Gross Unrealized Losses | (70) | (741)
Available-for-sale investments | 21,247 | $ 21,670
U.S. government-sponsored enterprises |  |
Debt Securities, Available-for-sale [Line Items] |  |
Amortized Cost | 77,173 |
Gross Unrealized Gains | 160 |
Gross Unrealized Losses | 0 |
Available-for-sale investments | $ 77,333 |

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- Definition Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563 + Details
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- Definition Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563 + Details
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- Definition Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=118942338&loc=SL82898722-210454 + Details
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